1. Field of the Invention
The present invention relates to a hydraulic jar mechanism incorporating valve means for automatic tripping of the mechanism to prevent failure of the tool by tensile overload.
2. Description of The Prior Art
Various types of fishing jars are employed for removing some tool or tubular member or other object from a well bore in the earth. The object stuck in the well bore is commonly referred to as a "fish" and fishing jars are run at the lower end of a string of drill pipe or tubing which ordinarily is referred to as the fishing, running or working string and the fishing tool is engaged with the lower end thereof. The fishing tool may be a spear, or overshot or similar device adapted to engage the "fish" so that the fish may be jarred loose by the jar and thereafter retrieved from the well bore.
Jars are employed for the purpose of applying hammer blows to aid in releasing the stuck fish while the fishing string is under tension. Jars of the hydraulic type, in general, are quite well known and comprise telescoping members. When telescoped, a pressure chamber containing a quantity of hydraulic fluid resists elongation of the jar. However, when an upward strain or tension is applied to the running string, the hydraulic fluid is compressed and bleeds through a restricted flow passage thus permitting a gradual telescoping of the tool until a large by-pass is opened and the induced pressure on the hydraulic fluid is instantaneously released. Since the fishing string is no longer resisted by the compressed fluid, the jar telescopes rapidly until such telescoping is stopped by engagement of a hammer and anvil that form part of the fishing jar.
Fishing jars presently employed can deliver various amounts of upward impacts or jarring loads to the fish; however, with all fishing jars presently known to applicant, it is possible to inadvertently or intentionally overload the jar and exceed the tensile strength of the particularly designed tool, resulting in the tool bursting, parts collapsing and/or seals being destroyed.
One object of the present invention is to provide a hydraulic jar wherein the tripping or actuating mechanism is functionally insensitive to an amount of load applied to the jar in excess of the design limits of the tool.
Another object of a preferred form of the present invention is to provide a hydraulic fishing jar which, under application of normal load, has a constant time delay regardless of the load applied to the fishing jar within the range of the design limitations of the particular size jar and incorporates the pressure relief mechanism for protection against tensile overload.
Yet a further object of the present invention is to provide a fishing jar for removing stuck objects from a well bore in which hydraulic fluid within a compression chamber is compressed by the jar load through the tool which may, in fact, exceed the recommended operating load strength of the tool, but which may not, of course, exceed the tensile of the tool, without requiring any initial setting or adjustment by an operator at the earth's surface, or any adjustment of the hydraulic jar once it is in operation.
Yet a further object of the present invention is to provide a fishing jar for removing stuck objects from a well bore in which hydraulic fluid within a compression chamber is compressed by a tensile load either within or exceeding the maximum recommended operating load of the jar without requiring any initial setting or adjustment by an operator at the earth's surface, or any adjustment of the hydraulic jar once it is in operation and wherein such jar includes spaced cross sectional areas in the chamber of a different size which are responsive to the compressed hydraulic fluid for passing the compressed hydraulic fluid through a flow regular by-pass means and, when the maximum allowable load is approached, a pressure relief mechanism, to effect movement of a piston to open a valve and release the compressed hydraulic fluid through a by-pass so that a jar may be applied to the fish.
Yet a further object of the present invention is to provide a fishing jar for removing stuck objects from a well bore in which hydraulic fluid within a compression chamber is compressed by a piston to the jar load applied through the tool without requiring any initial setting by an operator at the earth's surface, or any adjustment of the hydraulic jar once it is in operation and wherein such jar includes spaced cross sectional areas in the chamber of a different size which are responsive to the compressed hydraulic fluid for passing the compressed hydraulic fluid through a flow by-pass means and a pressure relief mechanism in a piston to effect movement of the piston to manipulate a valve and release the compressed hydraulic fluid so that a jar may be applied to the fish, said spaced cross sectional areas being of a predetermined relationship for controlling the compressed hydraulic fluid pressure differential in the chamber acting through the flow by-pass means and the pressure relief valve to move the piston with a minimum of pressure differential in the compression chamber acting through the flow by-pass means and the relief valve and with a minimum metering stroke of the jar.
Still another object of the present invention is to provide a hydraulic jar of relatively simple construction which should be normally substantially foolproof to tolerate any amount of load attempted to be applied to the tool.
Other objects and advantages of the present invention will become apparent from the following description and drawings.